Radio communication apparatus and its reception timing estimating method

ABSTRACT

A radio communication apparatus includes a low-rate clock oscillator for generating a low-rate clock signal used for reception timing estimation; a frequency deviation measuring duration controller for determining a deviation measuring duration of measuring a frequency deviation of the low-rate clock signal in accordance with an intermittent time interval of the radio signal; a frequency deviation measuring section for measuring the frequency deviation of the low-rate clock signal over the deviation measuring duration; and a timing counter for correcting the frequency deviation of the low-rate clock signal, for measuring an intermittent span of the received signal in response to the low-rate clock signal after the correction, and for generating the estimated reception timing of the radio signal.

TECHNICAL FIELD

[0001] The present invention relates to a radio communication apparatusand its reception timing estimating method for estimating receptiontiming of a radio signal which is intermittently transmitted atspecified time intervals in a radio communication system.

BACKGROUND ART

[0002] Conventional radio communication systems widely employ a schemeof intermittently transmitting a control signal such as systembroadcasting information and paging information to mobile equipment atspecified time intervals. The mobile equipment of such a radiocommunication system has a low-rate clock oscillator with small powerconsumption and low oscillation frequency such as an RTC (Real TimeClock), and a high-rate clock oscillator oscillating at a high frequencyat high frequency stability such as a TCXO (Temperature CompensatedCrystal Oscillator). The mobile equipment measures the transmission timeinterval of the control signal in response to the output of the low-rateclock oscillator, and estimates the reception timing. In addition, itbrings the high-rate clock oscillator into operation only in proximityof the estimated desired reception timing to receive the control signaltransmitted intermittently. With such a configuration, the mobileequipment enables the high-rate clock oscillator with rather large powerconsumption to operate intermittently in synchronization with thetransmission timing of the control signal, thereby reducing the powerconsumption in an incoming call waiting state and the like.

[0003] As the low-rate clock oscillator used for the reception timingestimation, an oscillator with low power consumption and low frequencyis usually selected. However, such an oscillator usually has a frequencydeviation up to about 100 ppm. Thus, its frequency stability is vastlyinferior to that of the high-rate clock oscillator of about a few partsper million. Therefore, to estimate the reception timing of the controlsignal accurately in response to the output of the low-rate clockoscillator, it is necessary to measure the frequency of the low-rateclock oscillator deviation in advance, and to correct the frequencydeviation before estimating the reception timing in response to thelow-rate clock signal after the correction.

[0004]FIG. 1 is a block diagram showing a configuration of mobileequipment employing a conventional frequency deviation estimating methodof a low-rate clock signal, which is disclosed in Japanese patentapplication laid-open No. 2000-13269, for example. The operation of theconventional mobile equipment will be described.

[0005] First, a high-rate clock oscillator 1 generates an operationclock signal 102 with a high frequency and small frequency deviation,and supplies it to a timing controller 103 and to another receivedsignal processing section to be used for the signal receptionprocessing, not shown in FIG. 1. In contrast, a low-rate clockoscillator 2 generates a timing clock signal 109 with a low frequencyand large frequency deviation.

[0006] A PLL 104, receiving the operation clock signal 102, increasesits frequency by a specified scaling factor, and outputs a deviationmeasuring clock signal 105.

[0007] In response to a frequency deviation measuring instruction 113 ofthe timing clock signal 109 output from the timing controller 103, ameasuring duration control counter 110 instructs the deviation measuringcounter 106 to start counting the number of the clock pulses of thedeviation measuring clock signal 105. At the same time, the measuringduration control counter 110 starts counting the number of clock pulsesof the timing clock signal 109. The measuring duration control counter110 has the number of clock pulses of the timing clock signal 109 fordefining the duration of the frequency deviation measurement (called“deviation measuring clock number” from now on).

[0008] The deviation measuring clock number is set such that desiredmeasurement accuracy is obtained as a result of the frequency deviationmeasurement. For example, to achieve the frequency deviation measurementat the accuracy of one millionth of the timing clock signal 109, asuitable deviation measuring clock number is set such that the frequencydeviation measuring duration, which is defined by the period of thetiming clock signal 109 and the deviation measuring clock number,becomes one million times the period of the deviation measuring clocksignal 105.

[0009] Since the frequency of the deviation measuring clock signal 105is multiplied by the PLL 104, the frequency deviation measuring durationcan be reduced by increasing the multiplication number of the PLL 104.The power consumption of the PLL 104, however, increases with themultiplication number of the deviation measuring clock signal 105.

[0010] When the number of clock pulses of the timing clock signal 109 iscounted up to the deviation measuring clock number, the measuringduration control counter 110 instructs the deviation measuring counter106 to stop counting the number of the clock pulses of the deviationmeasuring clock signal 105, and notifies the timing controller 103 ofthe completion of the frequency deviation measurement.

[0011] Subsequently, the timing controller 103 reads the count value ofthe deviation measuring counter 106 as to the deviation measuring clocksignal 105, and calculates the frequency deviation 115 of the timingclock signal 109 in response to the count value.

[0012] The calculated frequency deviation 115 of the timing clock signal109 is supplied to a reset counter 114 for generating an estimatedreception timing to be used for the frequency deviation correction ofthe timing clock signal 109.

[0013] With the foregoing configuration, the conventional radio receiverdetects the frequency deviation of the timing clock signal 109 using thedeviation measuring clock signal 105 the PLL 104 generates bymultiplying the frequency of the operation clock signal 102, therebyreducing the frequency deviation measuring duration. Accordingly, it isnecessary for the conventional radio receiver to include the PLL 104 formultiplying the frequency of the operation clock signal 102. Thispresents a problem of increasing the circuit scale and the powerconsumption for the frequency deviation measurement.

[0014] The present invention is implemented to solve the foregoingproblems. Therefore it is an object of the present invention to providea radio communication apparatus and its reception timing estimatingmethod capable of estimating the reception timing of the radio signalwhich is transmitted intermittently, at high accuracy by measuring thefrequency deviation of the timing clock signal used for generating theestimated reception timing at high accuracy with curbing an increase ofthe power consumption.

DISCLOSURE OF THE INVENTION

[0015] According to one aspect of the present invention, the radiocommunication apparatus is configured such that it determines adeviation measuring duration of measuring a frequency deviation of a lowfrequency, low frequency stability timing clock signal in accordancewith an intermittent time interval of a radio signal, a target signal tobe received.

[0016] Thus, when it is expected that the intermittent time interval islong and the estimation error of the reception timing of the radiosignal is large, the radio communication apparatus can lengthen thedeviation measuring duration to improve the resolution of measuring thefrequency deviation of the timing clock signal. As a result, it cancorrect the frequency of the timing clock signal in response to thefrequency deviation measured, thereby offering an advantage of beingable to increase the estimation accuracy of the reception timing of theradio signal.

[0017] In contrast, when it is expected that the intermittent timeinterval of the radio signal is short and the estimation error of thereception timing of the radio signal is small, the radio communicationapparatus can shorten the deviation measuring duration. Thus, it offersan advantage of being able to curb an increase in the power consumptionrequired to carry out the measurement processing of the frequencydeviation of the timing clock signal.

[0018] The radio communication apparatus in accordance with the presentinvention can be configured such that it includes a reception timingdetector for detecting a reception timing of the radio signal, and thata frequency deviation measuring duration controller detects anestimation error between an estimated reception timing generated by atiming counter and the actual reception timing of the radio signal, anddecides the deviation measuring duration to be used in a subsequentfrequency deviation measurement in accordance with the estimation error.

[0019] Thus, when a decision is made that continuing the intermittentreception processing of the radio signal will be difficult because of alarge estimation error, the radio communication apparatus can lengthenthe measuring duration of the frequency deviation of the timing clocksignal to improve the resolution of measuring the frequency deviation ofthe timing clock signal. As a result, it can correct the frequency ofthe timing clock signal in response to the frequency deviation measured,thereby offering an advantage of being able to increase the estimationaccuracy of the reception timing of the radio signal.

[0020] The radio communication apparatus in accordance with the presentinvention can be configured such that the frequency deviation measuringduration controller stores a maximum permissible value of the estimationerror of the reception timing, counts a number of times of continuouslyreceiving the radio signal in which the estimation error is greater thanthe maximum permissible value; and starts the measurement processing ofthe frequency deviation of the timing clock signal if the number oftimes of continuously receiving the radio signal exceeds a specifiedthreshold value.

[0021] Thus, it halts measuring the frequency deviation of the timingclock signal even if the frequency accuracy of the timing clock signaldeteriorates for a short time and the estimation error increases only ashort term. It automatically measures the frequency deviation of thetiming clock signal only when fluctuations in the frequency accuracy ofthe timing clock signal continue for a long time and a decision is madethat it is difficult to continue the intermittent reception of the radiosignal. Therefore it offers an advantage of being able to curb anincrease in the power consumption required for the frequency deviationmeasurement.

[0022] The radio communication apparatus in accordance with the presentinvention can be configured such that the frequency deviation measuringduration controller counts a number of times of continuously receivingthe radio signal in which the estimation error is greater than themaximum permissible value; and extends the measuring duration of thefrequency deviation of the timing clock signal if the count valueexceeds a specified threshold value.

[0023] Thus, it offers an advantage of being able increase theestimation accuracy of the reception timing of the radio signal byimproving the resolution of the frequency deviation of the timing clocksignal measurement, if fluctuations in the frequency accuracy of thetiming clock signal continue for a long time, and hence a decision ismade that continuing the intermittent reception of the radio signal isdifficult.

[0024] The radio communication apparatus in accordance with the presentinvention can be configured such that the frequency deviation measuringduration controller counts the number of times of continuously receivingthe radio signal in which the estimation error is less than the maximumpermissible value; and reduces the measuring duration of the frequencydeviation of the timing clock signal if the count value exceeds aspecified threshold value.

[0025] Thus, when a decision is made that the fluctuations in thefrequency deviation of the timing clock signal are small, the radiocommunication apparatus can automatically reduces the measuring durationof frequency deviation of the timing clock signal. Thus, it offers anadvantage of being able to reduce the power consumption required for thefrequency deviation measurement.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is a block diagram showing a configuration of aconventional frequency deviation estimating circuit;

[0027]FIG. 2 is a block diagram showing a configuration of an embodiment1 of the reception timing estimating circuit in accordance with thepresent invention;

[0028]FIG. 3 is a schematic diagram illustrating an operationenvironment of a radio communication apparatus incorporating theembodiment 1 of the reception timing estimating circuit in accordancewith the present invention;

[0029]FIG. 4 is a diagram showing a frequency deviation measuringduration table of the embodiment 1 in accordance with the presentinvention;

[0030]FIG. 5 is a block diagram showing a configuration of an embodiment2 of the reception timing estimating circuit in accordance with thepresent invention; and

[0031]FIG. 6 is a block diagram showing a configuration of an embodiment3 of the reception timing estimating circuit in accordance with thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0032] The best mode for carrying out the invention will now bedescribed with reference to the accompanying drawings to explain thepresent invention in more detail.

[0033] Embodiment 1

[0034]FIG. 2 is a block diagram showing a configuration of an embodiment1 of the reception timing estimating circuit in accordance with thepresent invention. In FIG. 2, the reference numeral 1 designates ahigh-rate clock oscillator (first oscillator) that includes a TCXO andgenerates a high frequency operation clock signal with high frequencystability; 2 designates a low-rate clock oscillator (second oscillator)that includes an RTC and generates a timing clock signal with lowfrequency stability, the frequency of which is lower than that of theoperation clock signal; and 3 designates a timing controller forestimating the reception timing of the radio signal in response to thetiming clock signal, and for controlling the start and stop of thehigh-rate clock oscillator 1.

[0035] In the timing controller 3, the reference numeral 5 designates afrequency deviation measuring section for measuring the frequencydeviation of the timing clock signal in response to the operation clocksignal; 6 designates a measuring duration management section formeasuring the frequency deviation measuring duration in response to thetiming clock signal, and for instructing the frequency deviationmeasuring section 5 to start or stop the deviation measurement; and 7designates a reference timing counter (timing counter) for correctingthe frequency deviation of the timing clock signal, which is measured bythe frequency deviation measuring section 5, and for generating acontrol signal of the high-rate clock oscillator by estimating thereception timing of the radio signal.

[0036] The reference numeral 8 designates a measuring durationcontroller (frequency deviation measuring duration controller) forcarrying out the communication control processing of the radiocommunication apparatus, and for controlling the timing controller 3;and 9 designates a frequency deviation measuring duration table forprestoring the frequency deviation measuring duration managed by themeasuring duration management section 6.

[0037]FIG. 3 is a schematic diagram illustrating an operationenvironment of the radio communication apparatus incorporating theembodiment 1. In FIG. 3, the reference numeral 10 designates a basestation that transmits a control signal such as a paging and systembroadcasting information at every specified transmission intervalT_(int); and 11 designates a radio communication apparatus thatincorporates the reception timing estimating circuit as shown in FIG. 2,and receives the control signal transmitted from the base station 10.

[0038] The base station 10 transmits the control signal by switching thetransmission interval T_(int) in response to the total number of theradio communication apparatuses installed in the radio communicationsystem and to the density of the communication requests. On the otherhand, the radio communication apparatus 11 continuously receives thecontrol signal transmitted from the base station 10 at everytransmission interval T_(int) to wait an incoming call or to monitor thesystem broadcasting information. The radio communication apparatus 11normally operates the low-rate clock oscillator 2 at small powerconsumption to reduce the power consumption. Thus, it estimates thereception timing of the control signal transmitted from the base station10 in response to the timing clock signal, and carries out the receptionprocessing of the control signal by intermittently activating thehigh-rate clock oscillator 1 with the large power consumption inresponse to the estimated reception timing.

[0039] Incidentally, the base station 10 transmits the transmissioninterval T_(int) of the control signal by incorporating it into thecontrol signal as the system broadcasting information. Receiving thecontrol signal, the radio communication apparatus 11 can recognize thetransmission interval T_(int) of the base station 10.

[0040] Next, the operation of the present embodiment 1 of the receptiontiming estimating circuit in the radio communication apparatus 11 willbe described.

[0041] First, at the initial start of the radio communication apparatus11, the measuring duration controller 8 carries out the receptionprocessing of the control signal continuously for a period of timesufficiently longer than the maximum value of the transmission intervalT_(int) of the base station 10 to receive the control signal includingthe system broadcasting information. Subsequently, the measuringduration controller 8 reads the transmission interval T_(int) includedin the system broadcasting information. After that, every time the radiocommunication apparatus 11 receives the control information includingthe system broadcasting information, the measuring duration controller 8reads the transmission interval T_(int) so that the measuring durationcontroller 8 holds the latest transmission interval T_(int).

[0042] Subsequently, the timing controller 3 estimates the receptiontiming by counting the specified number of pulses of the timing clocksignal output from the low-rate clock oscillator 2. For example, assumethat the receiving interval T_(int)=720 msec, the frequency of thetiming clock signal 32 kHz, and the frequency deviation of the timingclock signal is zero. Then, the timing controller 3 can generate thetransmission interval T_(int) by counting 23040 pulses of the timingclock signal. Accordingly, it can estimate the next reception timing ofthe control signal by causing the reference timing counter 7 to countthe specified number of pulses of the timing clock signal from the timethe measuring duration controller 8 starts receiving the control signal.

[0043] However, since the timing clock signal the low-rate clockoscillator 2 outputs has usually low frequency stability, estimating thereception timing by simply counting the specified number of pulses ofthe timing clock signal will cause an estimation error ΔT between theactual transmission interval T_(int) and the estimated reception timing.The estimation error ΔT increases in proportion to the length of thetransmission interval T_(int) to be estimated.

[0044] Before instructing the high-rate clock oscillator 1 to stop theoperation clock signal, the timing controller 3 and measuring durationcontroller 8 measure the frequency deviation of the timing clock signalin response to the operation clock signal, and corrects the estimationerror ΔT in accordance with the frequency deviation. The frequencydeviation measurement processing of the timing clock signal by thetiming controller 3 will be described below.

[0045] First, the measuring duration controller 8 determines thefrequency deviation measuring duration T_(ref), the period of time formeasuring the frequency deviation. The frequency deviation of the timingclock signal is calculated by counting the number of pulses of thetiming clock signal and that of the operation clock signal with the highfrequency decision accuracy output from the high-rate clock oscillator 1for the frequency deviation measuring duration T_(ref), and by comparingthe two count values. Since the measurement resolution of the frequencydeviation of the timing clock signal is improved in proportion to thefrequency deviation measuring duration T_(ref), it is preferable thatthe frequency deviation measuring duration T_(ref) be set as long aspossible from the viewpoint of the measurement accuracy of the frequencydeviation.

[0046] On the other hand, to conduct the frequency deviationmeasurement, since the timing controller 3 must receive the operationclock signal during the frequency deviation measuring duration T_(ref),both the high-rate clock oscillator 1 and low-rate clock oscillator 2must be operated. Consequently, from the viewpoint of reducing the powerconsumption of the radio mobile equipment, it is preferable that thefrequency deviation measuring duration T_(ref) be set as short aspossible.

[0047] Thus, the measuring duration controller 8 pay attention to theforegoing fact that the expected value of the estimation error ΔT of thereception timing increases in proportion to the transmission intervalT_(int). Thus, when the base station 10 sets a long transmissioninterval T_(int) (when the expected value of the estimation error ΔT islarge), the frequency deviation measuring duration T_(ref) is lengthenedto enable the frequency deviation of the timing clock signal to bemeasured at a high resolution. On the contrary, when the base station 10sets a short transmission interval T_(int) (when the expected value ofthe estimation error ΔT is small), the frequency deviation measuringduration T_(ref) is shortened to reduce the power consumption of thefrequency deviation measurement.

[0048] To determine the frequency deviation measuring duration T_(ref),the measuring duration controller 8 stores in advance the frequencydeviation measuring duration table 9 that provides the relationshipsbetween the transmission interval T_(int) and the frequency deviationmeasuring duration T_(ref) as shown in FIG. 4, for example.

[0049] The frequency deviation measuring duration table 9 stores aplurality of transmission intervals T_(int). The transmission intervalsT_(int) are assumed to be decided at the system design stage of thecommunication system.

[0050] As for the frequency deviation measuring durations T_(ref)corresponding to the plurality of transmission intervals T_(int), theyare given appropriate values to achieve desired resolution of thefrequency deviation measurement for measuring the expected estimationerror ΔT of the transmission intervals T_(int).

[0051] Receiving the control signal and reading the transmissioninterval T_(int) determined by the base station, the measuring durationcontroller 8 refers to the frequency deviation measuring duration table9, and reads the frequency deviation measuring duration T_(ref)corresponding to the transmission interval T_(int). For example, whenthe base station 10 sets the transmission interval at T_(int)=720 msec,the measuring duration controller 8 selects the frequency deviationmeasuring duration T_(ref) of 50 msec.

[0052] Subsequently, the measuring duration controller 8 supplies thefrequency deviation measuring duration T_(ref) thus selected to themeasuring duration management section 6 of the timing controller 3, andinstructs it to start the measurement of the frequency deviation of thetiming clock signal.

[0053] Receiving the instruction on starting the frequency deviationmeasurement, the measuring duration management section 6 divides thefrequency deviation measuring duration T_(ref) by the nominal period ofthe timing clock signal (31.25 μsec when the nominal frequency is 32kHz), thereby calculating a deviation measuring clock number K.

[0054] Subsequently, the measuring duration management section 6 sendsto the frequency deviation measuring section 5 the count startinstruction on the operation clock signal, and starts counting thenumber of pulses of the timing clock signal at the same time. Thefrequency deviation measuring section 5, receiving the count startinstruction, starts counting the number of pulses of the operation clocksignal.

[0055] When completing the counting of the deviation measuring clocknumber K, the measuring duration management section 6 supplies thefrequency deviation measuring section 5 and reference timing counter 7with the count stop instruction of the operation clock signal. Thus, thefrequency deviation measuring section 5 supplies the reference timingcounter 7 with the number of pulses K_(res) of the operation clocksignal counted from the count start instruction to the count stopinstruction.

[0056] On the other hand, receiving the count stop instruction on theoperation clock signal from the measuring duration management section 6,the reference timing counter 7 reads the number of pulses K_(res) of theoperation clock signal from the frequency deviation measuring section 5,and calculates the frequency deviation of the timing clock signal Δffrom the frequency of the operation clock signal and the deviationmeasuring clock number K according to the following Eq. 1.

Δf=(K/K _(res))·f _(h) −f ₁  Eq. 1.

[0057] where f_(h) is the frequency of the operation clock signal, andf₁ is the nominal frequency of the timing clock signal.

[0058] When completing the calculation of the frequency deviation Δf,the reference timing counter 7 stops the oscillation of the high-rateclock oscillator 1.

[0059] Subsequently, the reference timing counter 7 corrects thefrequency of the timing clock signal in accordance with the frequencydeviation Δf. Then, it measures the transmission interval T_(int) inaccordance with the timing clock signal corrected, and estimates thenext reception timing of the control signal. As a result, in synchronismwith the estimated reception timing, the reference timing counter 7controls the start and stop of the oscillation of the high-rate clockoscillator 1, thereby controlling the intermittent output of theoperation clock signal.

[0060] If the base station 10 sends the instruction on the change of thetransmission interval T_(int) during the intermittent receptionprocessing of the control signal, the measuring duration controller 8determines the frequency deviation measuring duration T_(ref)corresponding to the transmission interval T_(int) after the change withreference to the frequency deviation measuring duration table 9, andinstructs the measuring duration management section 6 to measure thefrequency deviation of the timing clock signal. Receiving theinstruction, the measuring duration management section 6 starts thehigh-rate clock oscillator 1 via the reference timing counter 7 tomeasure the frequency deviation Δf of the timing clock signal again inresponse to the frequency deviation measuring duration T_(ref) correctedby the method as described above. Then, the reference timing counter 7carries out the frequency correction of the timing clock signal inaccordance with the frequency deviation Δf obtained as a result of theremeasurement, and estimates the reception timing.

[0061] In this way, the present embodiment 1 of the reception timingestimating circuit automatically switches the measuring duration T_(ref)for calculating the frequency deviation Δf of the timing clock signalwith the low frequency stability in accordance with the transmissioninterval T_(int) of the control signal set by the base station 10.Accordingly, when the transmission interval T_(int) is long and theestimation error ΔT of the reception timing is expected to be large, thefrequency deviation measuring duration T_(ref) is lengthened to increasethe measurement resolution of the frequency deviation Δf and to improvethe accuracy of the frequency deviation measurement. In contrast, whenthe transmission interval T_(int) is short and the estimation error ΔTof the reception timing is expected to be small, the frequency deviationmeasuring duration T_(ref) is shortened to curb an increase of the powerconsumption required for the measurement processing of the frequencydeviation Δf.

[0062] In the present embodiment 1, although the measuring durationcontroller 8 instructs to measure the frequency deviation of the timingclock signal at the start of the radio communication apparatus and atthe change of the transmission interval T_(int) by the base station 10,this is not essential. For example, a configuration is also possible inwhich the measuring duration controller 8 includes a timer so that themeasurement processing of the frequency deviation of the timing clocksignal is carried out at specified time intervals.

[0063] In addition, although the present embodiment is configured suchthat the measuring duration controller 8 has the frequency deviationmeasuring duration table 9 recording the frequency deviation measuringdurations T_(ref) corresponding to the plurality of transmissionintervals T_(int), and changes the frequency deviation measuringduration T_(ref) in response to the transmission interval T_(int) withreference to the frequency deviation measuring duration table 9, thedecision scheme of the frequency deviation measuring duration T_(ref) isnot limited to such a method. For example, a method can also be employedwhich calculates the frequency deviation measuring duration T_(ref) bymultiplying the transmission interval T_(int) by a specifiedtransformation coefficient. Alternatively, a method can also be usedsuch as calculating the frequency deviation measuring duration T_(ref)by applying other mathematical expressions to the transmission intervalT_(int).

[0064] Embodiment 2

[0065] In the foregoing embodiment 1, the measuring duration. controller8 includes the frequency deviation measuring duration table 9, anddetermines the frequency deviation of the timing clock signal measuringduration T_(ref) in accordance with the transmission interval T_(int) ofthe control signal set by the frequency base station 10. In the presentembodiment 2, the measuring duration controller 8 compares the receptiontiming the timing controller 3 estimates in response to the timing clocksignal after the frequency deviation correction with the timing at whichthe control signal is actually received, detects the estimation errorbetween the two timings, and measures the frequency deviation of thetiming clock signal by lengthening the frequency deviation measuringduration T_(ref) when the estimation error is greater than a specifiedthreshold value.

[0066] The present embodiment 2 differs from the foregoing embodiment 1only in that it includes a reception timing detector for detecting thereception timing of the control signal, calculates the estimation errorbetween the estimated reception timing and the actual reception timingof the control signal, and determines the frequency deviation measuringduration T_(ref) in accordance with the estimation error. Since theremaining configuration is identical, the description thereof is omittedby using the same reference numerals.

[0067]FIG. 5 is a block diagram showing a configuration of the presentembodiment 2 of the reception timing estimating circuit. In FIG. 5, thereference numeral 20 designates a reception timing detector forreceiving the received signal demodulated by the signal receivingsection (not shown in FIG. 5) of the radio communication apparatus, andfor detecting the control signal in the received signal.

[0068] Next, the operation of the present embodiment 2 of the receptiontiming estimating circuit will be described. First, the reception timingdetector 20, receiving the received signal demodulated by the signalreceiving section (not shown in FIG. 5), detects a specified detectionword inserted into the received signal to identify the control signal,and supplies the reception timing of the detected control signal to themeasuring duration controller 8.

[0069] On the other hand, according to the method of the foregoingembodiment 1, the reference timing counter 7 of the timing controller 3generates the estimated reception timing in response to the timing clocksignal after passing through the frequency deviation correction.

[0070] The measuring duration controller 8 receives the estimatedreception timing and the actual reception timing of the control signalthe reception timing detector 20 outputs, and detects the estimationerror ΔT of the reception timing. The measuring duration controller 8,which stores a maximum permissible value ΔT_(max) of the estimationerror of the reception timing in advance, compares the estimation errorΔT with the maximum permissible value ΔTmax. When the estimation errorΔT is greater than the maximum permissible value ΔT_(max), the measuringduration controller 8 lengthens the frequency deviation measuringduration T_(ref) which has been determined with reference to thefrequency deviation measuring duration table 9 shown in FIG. 4.

[0071] For example, consider the case where the receiving interval isset at T_(int)=720 msec and the frequency deviation measuring durationT_(ref)=50 msec is selected. If the estimation error ΔT exceeds themaximum permissible value ΔT_(max), the measuring duration controller 8lengthens the frequency deviation measuring duration T_(ref) by 20% toT_(ref)=60 msec, for example, and notifies the measuring durationmanagement section 6 of it.

[0072] As for the maximum permissible value ΔT_(max), it is assumed herethat an appropriate value is set considering the startup time of thesignal receiving section (not shown in FIG. 5), which is required fromthe start of the high-rate clock oscillator 1 to the time enabling theradio communication apparatus to receive the control signal.

[0073] Subsequently, the measuring duration controller 8 instructs themeasuring duration management section 6 to measure the frequencydeviation of the timing clock signal. The measuring duration managementsection 6 and frequency deviation measuring section 5 measure thefrequency deviation using the lengthened frequency deviation measuringduration T_(ref) in the same manner as the foregoing embodiment 1, andsupplies the frequency deviation to the reference timing counter 7.Thus, the reference timing counter 7 corrects the timing clock signal inaccordance with the frequency deviation, and generates the estimatedreception timing, in response to which the start/stop of the high-rateclock oscillator 1 is controlled.

[0074] As described above, the present embodiment 2 of the receptiontiming estimating circuit is configured such that it includes thereception timing detector 20 for detecting the actual reception timingof the control signal which is transmitted intermittently, and that whenthe estimation error ΔT between the estimated reception timing generatedby the reference timing counter and the actual reception timing of thecontrol signal is greater than the maximum permissible value ΔT_(max),the measuring duration controller 8 extends the frequency deviationmeasuring duration T_(ref) and instructs the measurement of thefrequency deviation of the timing clock signal. Accordingly, if thecorrect estimation of the reception timing cannot be carried out becauseof an increase in the fluctuations in the frequency of the low-rateclock oscillator 2 due to variations in the environment in which theradio communication apparatus is used such as the variation in theambient temperature, for example, the present embodiment automaticallyextends the frequency deviation measuring duration T_(ref) to enable themeasurement of the frequency deviation of the timing clock signal at ahigher measurement resolution, thereby being able to maintain theaccuracy of the estimation of the reception timing by the referencetiming counter 7.

[0075] Although the measuring duration controller 8 extends thefrequency deviation measuring duration T_(ref) by 20% when theestimation error of the estimated reception timing ΔT is greater thanthe maximum permissible value ΔT_(max) in the present embodiment 2, anextension amount of the frequency deviation measuring duration T_(ref)is not limited to 20%. It can be any suitable value for obtaining thedesired resolution of the frequency deviation measurement accuracy whenthe estimation error ΔT is increased.

[0076] Embodiment 3

[0077] In the foregoing embodiment 2, the measuring duration controller8 instructs to measure the frequency deviation when the estimation errorΔT of the estimated reception timing the reference timing counter 7generates is greater than the maximum permissible value ΔT_(max). Incontrast with this, in the present embodiment 3, the measuring durationcontroller 8 measures the number of times of continuously receiving thecontrol signal in which the estimation error ΔT is greater than themaximum permissible value ΔT_(max), and the number of times ofcontinuously receiving the control signal in which the estimation errorΔT is equal to or less than the maximum permissible value ΔT_(max), andadjusts the frequency deviation measuring duration T_(ref) of the timingclock signal in response to the count values.

[0078] The present embodiment 3 differs from the foregoing embodiment 2only in that the measuring duration controller 8 includes counters eachfor measuring the number of times of continuously receiving the controlsignal, and adjusts the frequency deviation measuring duration inresponse to the count values. Since the remaining configuration isidentical, the description thereof is omitted by using the samereference numerals.

[0079]FIG. 6 is a block diagram showing a configuration of the presentembodiment 3 of the reception timing estimating circuit. In FIG. 6, thereference numeral 21 designates an error detection counter for measuringthe number of times of continuously receiving the control signal inwhich the estimation error ΔT of the estimated reception timing isgreater than the maximum permissible value ΔT_(max); and 22 designates anormal reception counter for measuring the number of times ofcontinuously receiving the control signal in which the estimation errorΔT is equal to or less than the maximum permissible value ΔT_(max).

[0080] Next, the operation of the present embodiment 3 of the receptiontiming estimating circuit will be described. First, according to themethod described in the foregoing embodiment 1, the measuring durationcontroller 8 determines the frequency deviation measuring durationT_(ref) with reference to the frequency deviation measuring durationtable 9. The measuring duration management section 6 and frequencydeviation measuring section 5 measure the frequency deviation of thetiming clock signal over the frequency deviation measuring durationT_(ref). The reference timing counter 7 carries but the frequencycorrection of the timing clock signal in response to the measurementresult, generates the estimated reception timing, and controls thestart/stop of the high-rate clock oscillator 1.

[0081] While the radio communication apparatus is receiving the controlsignal by intermittently operating the high-rate clock oscillator 1, themeasuring duration controller 8 compares the estimated reception timingthe reference timing counter 7 generates with the actual receptiontiming the reception timing detector 20 outputs every time the controlsignal is received, and calculates the estimation error ΔT of theestimated reception timing.

[0082] Subsequently, the measuring duration controller 8 compares theestimation error ΔT with the maximum permissible value ΔT_(max) of theestimation error. When the estimation error ΔT is greater than themaximum permissible value ΔT_(max), it makes a decision that thefrequency deviation of the timing clock signal exceeds the acceptablerange. Thus, it causes the error detection counter 21 to count up, andthe normal reception counter 22 to initialize its count value to zero atthe same time.

[0083] In contrast, when the estimation error ΔT is equal to or lessthan the maximum permissible value ΔT_(max), it makes a decision thatthe frequency deviation of the timing clock signal is within theacceptable range. Thus, it causes the normal reception counter 22 tocount up, and the error detection counter 21 to initialize its countvalue to zero at the same time.

[0084] With the foregoing configuration, the error detection counter 21hold the number of times of continuously receiving the control signal inwhich the estimation error ΔT is greater than the maximum permissiblevalue ΔT_(max). On the other hand, the normal reception counter 22 holdsthe number of times of continuously receiving the control signal inwhich the estimation error ΔT is less than the maximum permissible valueΔT_(max).

[0085] If the frequency deviation of the timing clock signal fluctuatesin connection with the variations in the environment in which the radiocommunication apparatus is used while the radio communication apparatusis receiving the control signal intermittently, the estimation error ΔTwill exceed the maximum permissible value ΔT_(max) continuously over aplurality of reception timings of the control signal, thereby increasingthe count value of the error detection counter 21.

[0086] The measuring duration controller 8 holds a threshold value K₁ ofthe number of times of continuously receiving the control signal formaking a decision as to whether to carry out the measurement of thefrequency deviation of the timing clock signal or not. If the countvalue of the error detection counter 21 exceeds the threshold valueK_(l), the measuring duration controller 8 extends the frequencydeviation measuring duration T_(ref) as in the foregoing embodiment 2,notifies the measuring duration management section 6 of the durationT_(ref), and instructs it to start the frequency deviation measurement.

[0087] As for the threshold value K₁, it is set at an appropriate valueto handle the variation in the environment in which the radiocommunication apparatus is used, such as the ambient temperature.

[0088] The frequency deviation measuring section 5 measures thefrequency deviation of the timing clock signal over the extendedfrequency deviation measuring duration T_(ref). After that, thereference timing counter 7 generates the estimated reception timing inresponse to the timing clock signal whose frequency deviation iscorrected. After the frequency deviation measurement, the estimationerror of the estimated reception timing ΔT decreases, and hence theestimation error ΔT becomes less than the maximum permissible valueΔT_(max). Thus, the count value of the normal reception counter 22increases.

[0089] The measuring duration controller 8 holds a threshold value K₂ ofthe number of times of continuously receiving the control signal formaking a decision as to whether the frequency deviation of the timingclock signal is stable or not. If the count value of the normalreception counter 22 exceeds the threshold value K₂, the measuringduration controller 8 makes a decision that the variation in theenvironment of the radio communication terminal is small, and hence thefluctuations in the frequency deviation of the timing clock signal aresmall. Thus, the measuring duration controller 8 shortens the extendedfrequency deviation measuring duration T_(ref) to the frequencydeviation measuring duration T_(ref) determined by the frequencydeviation measuring duration table 9.

[0090] As for the threshold value K₂, it is set at the number of timesof receiving the control signal during a sufficiently long period oftime such as a quarter, half or one hour in advance, which is longenough for making a decision as to the stability of the low-rate clockoscillator 2.

[0091] With such an arrangement, the present embodiment 3 haltsmeasuring the frequency deviation of the timing clock signal even if thefrequency accuracy of the timing clock signal deteriorates for a shorttime and the estimation error ΔT increases only a short term. Thepresent embodiment 3 measures the frequency deviation of the timingclock signal by automatically extending the frequency deviationmeasuring duration T_(ref) only when the frequency accuracy of thetiming clock signal fluctuates for a long time and the count value ofthe error detection counter 21 exceeds the specified threshold value K₁,and when it makes a decision that it is difficult to hold thesynchronization with the base station 10. Therefore the presentembodiment 3 can achieve the sufficient frequency deviation measurementresolution to correct the frequency deviation, and can curb an increasein the power consumption at the same time.

[0092] Furthermore, when the count value of the normal reception counter22 exceeds the threshold value K₂, the present embodiment 3 makes adecision that the frequency accuracy of the low-rate clock oscillator 2is stable and the fluctuations in the frequency deviation of the timingclock signal are small. In this case, the present embodiment 3automatically shortens the extended frequency deviation measuringduration T_(ref) to the specified initial value as described above.Thus, it can reduce the power consumption for the frequency deviationmeasurement processing thereafter.

[0093] Incidentally, although the present embodiment 3 is configuredsuch that when the count value of the normal reception counter 22exceeds the threshold value K₂, the measuring duration controller 8shortens the frequency deviation measuring duration T_(ref) to thefrequency deviation measuring duration T_(ref) determined according tothe frequency deviation measuring duration table 9, this is notessential. Such a configuration is also possible that shortens thefrequency deviation measuring duration T_(ref) by a specified ratio,only when the count value of the normal reception counter 22 exceeds thethreshold value K₂.

[0094] For example, in the case where the frequency deviation measuringduration is set at T_(ref)=50 msec, such a configuration is alsopossible in which the measuring duration controller 8 shortens thefrequency deviation measuring duration T_(ref) by 20% to T_(ref)=40 msecif the normal reception counter 22 exceeds the threshold value K₂.

[0095] Industrial Applicability

[0096] As described above, the radio communication apparatus and itsreception timing estimating method in accordance with the presentinvention are suitable for precisely estimating the reception timing ofthe radio signal which is transmitted intermittently, by measuring thefrequency deviation of the timing clock signal used for generating theestimated reception timing at high accuracy with curbing the increase inthe power consumption.

What is claimed is:
 1. A radio communication apparatus for carrying outreception processing of a radio signal which is transmittedintermittently at specified time intervals, said radio communicationapparatus comprising: a first oscillator for generating an operationclock signal used for the reception processing of the radio signal; asecond oscillator for generating a timing clock signal with apredetermined frequency lower than the frequency of the operation clocksignal; a frequency deviation measuring duration controller fordetermining a deviation measuring duration of measuring a frequencydeviation of the timing clock signal in accordance with an intermittenttime interval of the radio signal; a frequency deviation measuringsection for measuring the frequency deviation of the timing clock signalin response to the operation clock signal over the deviation measuringduration; and a timing counter for correcting the frequency deviation ofthe timing clock signal, for measuring an intermittent span of thereceived signal in response to the timing clock signal after thecorrection, and for starting said first oscillator in synchronizationwith an estimated reception timing of the radio signal.
 2. The radiocommunication apparatus according to claim 1, further comprising areception timing detector for detecting reception timing of the radiosignal actually received, wherein said frequency deviation measuringduration controller detects an estimation error of the estimatedreception timing against an actual reception timing, and decides thedeviation measuring duration to be used in a subsequent frequencydeviation measurement in accordance with the estimation error; and saidtiming counter corrects the frequency deviation of the timing clocksignal, generates the estimated reception timing of the radio signal bymeasuring the intermittent span of the received signal in response tothe timing clock signal after the correction, and starts the firstoscillator in synchronization with the estimated reception timing. 3.The radio communication apparatus according to claim 2, wherein saidfrequency deviation measuring duration controller further stores amaximum permissible value of the estimation error of the estimatedreception timing in advance, makes a decision as to whether theestimation error is greater than the maximum permissible value everytime of carrying out the reception processing of the radio signal, andcounts a number of times of continuously receiving the radio signal inwhich the estimation error is greater than the maximum permissiblevalue; and said frequency deviation measuring section has aconfiguration of measuring the frequency deviation of the timing clocksignal over a specified deviation measuring duration, if the number oftimes of continuously receiving the radio signal exceeds a specifiedthreshold value.
 4. The radio communication apparatus according to claim2, wherein said frequency deviation measuring duration controller has aconfiguration of storing a maximum permissible value of the estimationerror of the estimated reception timing in advance; making a decision asto whether the estimation error is greater than the maximum permissiblevalue every time of carrying out the reception processing of the radiosignal; counting a number of times of continuously receiving the radiosignal in which the estimation error is greater than the maximumpermissible value; and increases the deviation measuring duration bysaid frequency deviation measuring section in accordance with the numberof times of continuously receiving.
 5. The radio communication apparatusaccording to claim 2, wherein said frequency deviation measuringduration controller has a configuration of storing a maximum permissiblevalue of the estimation error of the estimated reception timing inadvance; making a decision as to whether the estimation error is lessthan the maximum permissible value every time of carrying out thereception processing of the radio signal; counting a number of times ofcontinuously receiving the radio signal in which the estimation error isless than the maximum permissible value; and decreases the deviationmeasuring duration by said frequency deviation measuring section inaccordance with the number of times of continuously receiving.
 6. Areception timing estimating method of a radio communication apparatusfor carrying out reception processing of a radio signal which istransmitted intermittently at specified time intervals, said receptiontiming estimating method comprising: an operation clock oscillation stepof generating an operation clock signal used for the receptionprocessing of the radio signal; a timing clock oscillation step ofgenerating a timing clock signal with a predetermined frequency lowerthan the frequency of the operation clock signal; a frequency deviationmeasuring duration control step of determining a deviation measuringduration of measuring a frequency deviation of the timing clock signalin accordance with an intermittent time interval of the radio signal; afrequency deviation measuring step of measuring the frequency deviationof the timing clock signal in response to the operation clock signalover the deviation measuring duration; and an estimated reception timinggenerating step of correcting the frequency deviation of the timingclock signal, of measuring an intermittent span of the received signalin response to the timing clock signal after the correction, and ofstarting the operation clock oscillation step in synchronization withthe estimated reception timing of the radio signal.
 7. A receptiontiming estimating method of a radio communication apparatus for carryingout reception processing of a radio signal which is transmittedintermittently at specified time intervals, said reception timingestimating method comprising: an operation clock oscillation step ofgenerating an operation clock signal used for the reception processingof the radio signal; a timing clock oscillation step of generating atiming clock signal with a predetermined frequency lower than thefrequency of the operation clock signal; a frequency deviation measuringstep of measuring a frequency deviation of the timing clock signal inresponse to the operation clock signal over a specified deviationmeasuring duration; an estimated reception timing generating step ofcorrecting the frequency deviation of the timing clock signal, ofgenerating an estimated reception timing of the radio signal bymeasuring an intermittent span of the received signal in response to thetiming clock signal after the correction, and of starting the operationclock oscillation step in synchronization with the estimated receptiontiming; a reception timing detection step of detecting a receptiontiming of an actually received radio signal; and a frequency deviationmeasuring duration control step of detecting an estimation error of theestimated reception timing against an actual reception timing, and ofdeciding the deviation measuring duration to be used in a subsequentfrequency deviation measurement in accordance with the estimation error.